Currently, in a long-term evolution (LTE) system, communication between terminal devices needs to be performed via a radio access network and a core network. As appearance of demands for many new traffics, and at the same time, in order to reduce a load of a network and achieve transfer of the load of the network, the communication between terminal devices has gradually become a new direction for studies. When a distance between two terminal devices is sufficiently near, the terminal device may discover existence of the counterpart, hence, direct communication between devices may be performed under control of an eNB.
In order to realize device to device communication, two types of air-interface resource allocation schemes, mode 1 and mode 2, are defined in an LTE-A (LTE-advanced) system. In mode 1, in order to avoid influencing reporting of a buffer status report (BSR) directed to a traffic of a conventional infrastructural communication mode, a mechanism of BSR directed to the device to device communication (which may be referred to as a ProSe BSR) is introduced, which mainly includes a triggering mechanism of a new BSR and an MAC signaling format and content of the BSR.
Currently, two ProSe BSR formats are defined for device to device (D2D) communication, which are shown in FIGS. 1 and 2, respectively. The two formats are both formats used for reporting ProSe BSRs in a case where there exist available to-be-transmitted data in ProSe destinations (sidelink destinations or sidelink targets). In other words, within a TTI transmitting ProSe BSRs, when all ProSe destinations have no data to be transmitted, UE is unable to determine which formats should be used by the reported ProSe BSRs.
A concept of a sidelink control period (briefly referred to as an SC period) is defined in the device to device (D2D) communication mode, the SC period referring to a time period containing scheduling control and transmission of data to which it corresponds. For mode 1, a basic operational principle of data transmission at a transmitter end in the D2D communication is as follows.
After scheduling of data transmission of a D2D user equipment (UE) is determined, an eNB transmits an SL grant (a sidelink grant) to the UE via a physical downlink control channel (PDCCH) scrambled by a sidelink radio network temporary identity (SL-RNTI), the SL grant containing time-frequency resource positions of scheduling control (SC) to be transmitted by the UE and time-frequency resource positions of data to be transmitted. A period of validity of the SL grant is one SC period, and an SC period to which it corresponds is a next SC period starting from 4 ms after a subframe transmitting the SL grant. After receiving an SL grant, the UE will first transmit the SC twice at a resource position of the SC indicated by the SL grant within the SC period to which the SL grant corresponds, and then transmit transport blocks (TBs) at resource positions of data indicated by the SL grant; wherein, each TB will be transmitted for four times, and the number of TBs that can be transmitted within one SC period is dependent on the number of resources allocated in the SL grant. FIG. 3 is a schematic diagram of the transmission process.
It should be noted that the above description of the background is merely provided for clear and complete explanation of this disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of this disclosure.